Wound magnetic core having staggered strips



Aug. 27, 1968 s. VADIM 3,399,365

WOUND MAGNETIC CORE HAVING STAGGERED STRIPS Filed Oct. 20, 1965 Var/I'mSubovici Attorney INVENTOR.

United States Patent "3,399,365 WOUND'MAGNETIC CORE HAVING STAGGEREDSTRIPS Subovici Vadim, Blvd. Republicii 58,

Bucharest, Rumania Filed Oct. 20, 1965, Ser. No. 498,816 Claimspriority, applicazigrgzliumania, Nov. 24, H64,

3 Claims. 61. 336-213) ABSTRACT OF THE DISCLOSURE A coiled magnetic coreis spirally wound from magnetic sheet material arranged in twojuxtaposed coextensive layers each composed of a plurality of parallelstrips with adjoining longitudinal edges, the widths of the individualstrips diliering in the two layers so that the gaps formed by theiradjoining edges are staggered in axial direction. There is alsodisclosed a method of coiling a -magnetic core by cutting a strip ofgrain-oriented magnetic sheet material into successive sections of equallength and successively bending them about a mandrel, with theirlongitudinal dimension parallel to the mandrel axis; the sheets may besoldered or welded to one another and may be annealed after coiling.

wound; this requires axial superposition of several such coils wheneverthe length of the core exceeds the width of the strips, thereby tendingto introduce additional air gaps. Also, the need for reducing thecurrent flow due to induced voltage dictates the formation of radialslits, to be filled with insulating material, whose presence decreasesthe mechanical strength of the core.

The principal object of this invention is to provide an improvedmagnetic core avoiding the aforestated disadvantages. Another object isto provide a process for making a core with relatively staggered gaps,avoiding the need for a separate slitting operation.

In accordance with an important feature of my invention, a magnetic coreis wound from two coextensive and juxtaposed layers of permeable sheetmaterial which are jointlycoiled about an axis, each layer consisting ofa plurality of parallel strips with adjoining longitudinal edges; thewidth of the strips in the two layers is so chosen that their adjoiningstrip edges are relatively staggered in axial direction. Thus, one layerconsists of n juxtaposed strip (n being equal to 2 or more) while theother layer contains m+l strips; in order to realize the largestpossible offset between the longitudinal gaps of the two layers, Iprefer to make the first layer from strips of a given width and thesecond layer from one or more inner strips of the same width and twoouter strips half that wide.

According to another aspect of this invention, I cut an elongate stripofgrain-oriented penmeable sheet material into a succession of sections ofthe same length, corresponding to the height of the core to be made, andform a spirally wound core body by successively bending these sectionsabout an axis which is parallel to their dimension of length; since thesections are cut from the same strip, they will generally be of likewidth but the axially extending gaps therebetween will not coincide, byreason of the increasing radius of the coiled sheet sections.

Patented Aug. 27, 1968 The invention will be described in greater detailwith reference to the accompanying drawing in which:

FIG. 1 is a perspective view of a pair of juxtaposed multistrip layerspartly wound intoa core according to the invention;

FIG. 2 is a view similar to FIG. 1, showing a modified core; and

FIG. 3 is a top plan view of an assembly for producing the core of FIG.2. v p

In FIG. 1, I have shown a transformer core 10 in the process of beingwound from two juxtaposed layers 11, 12 of sheet steel. Layer 11consists of two parallel strips 11a, 11b of given width A which is equalto half the axial length or height of the core. Layer 12 consists ofthree parallel strips 12a, 12b, 120, the central strip 12b having thewidth A whereas the two outer strips 12a, have only the width a/Q. sothat the total width of that layer also equals 2A. As a result of thisdimensioning, the longitudinal gaps between strips 12a,;1 2b and strips12b, 12c are axially staggered, by a distance A/2, with reference to thegap between strips 11a and 11b. Regardless of the number of strips ineach layer, the halfwidth strips 12a, 12c are always at the outer edges.

As further shown in FIG. 1, the two-layer turns of core 10 are separatedby a spiral clearance 13 forming axially extending voids for thecirculation of a cooling medium.

The completed core may be annealed in a neutral atmosphere, for therelief of bending stresses, and may be stabilized by suitablereinforcements, not shown. Its structure is practically monolithic andfree from radial air gaps.

The modified core 20 of FIG. 2 is wound from a single layer composed ofa succession of steel sheets 5, these sheets are sections of uniformlength L cut from a strip of width W. The strip may have been rolledwith its crystals or grains oriented in the longitudinal direction L,thus in a direction parallel to the coil axis 0. The sheets 5 may bejoined togethed for continuity, eg by soldering or welding as indicatedat 6. A spiral clearance 23 again forms a channel for the circulation ofa cooling medium.

FIG. 3 shows a device for producing the core 20 of FIG. 2. The devicecomprises a flexible endless element 1, such as a belt, band or cord,wound about three rollers 4, 4', 4" and a mandrel 3, represented by afurther roller, whose sense of rotation has been indicated by an arrowR. Mandrel 3 is shiftable in two directions, as indicated by an arrow S,and is under constant stress to maintain the band 1 taut. Therectangular sheets or strip sections 5 are introduced, one after theother, into the gap between band 1 and mandrel 3 so as to bend about themandrel axis and form an Archimedean spiral. When the necessary numberof sheets have been thus assembled into a coil, the resulting cylinderbody may be temporarily held in position by clamping rings or wire andis then annealed whereupon the retaining means can be replaced bypermanent reinforcements. The gaps between successive sheets, which maybe soldered or welded together as noted above, will generally notregister on successive turns of the coiled body 20.

The device shown in FIG. 3 may be supplemented by suitable means forlaterally guiding the sheets, for welding or soldering them, forstraightening their edges and for applying the retaining means.

It will thus be seen that I have provided va magnetic core whose axiallength is not limited by the width of the steel strip from which it ismade.

I claim:

1. A cylindrical magnetic core comprising a pair of juxtaposed andcoextensive layers of magnetically permeable sheet material woundtogether about an axis, each with adjoining longitudinal edges, theadjoining strip edges within said layer being relatively staggered inaxial direction.

2. A core as defined in claim 1 wherein one of said layers consists of nstrips and the other of saidlayers consists of n+1 strips, all of saidstrips having the same axial width except for a pair of outer strips ofsaid other layer, said outer strips being half as wide as all the otherstrips. i

3. Acore as defined in claim 1 wherein said layers are jointly wound inradially spaced turns forming axially extending voids for thecirculation of a cooling mediuin of said'laye'r's consisting ofa'plurality'of' parallel "strips 'Re fe i nc'e's Cit'ed UNITED STATESPATENTS Steinniaye'r etall 10 LARAM-IE E. AsrgN,

flier. D. A. TONE, Assistant Examiner. j

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,399,365 August 27, 1968 Vadim Subovici It is certified that errorappears in the above identified patent and that said Letters Patent arehereby corrected as shown below:

In the sheet of drawings, line 1, "S. VADIM" should read V. SUBOVICI Inthe heading to the printed specification, line 4, "Subovici Vadim"should read Vadim Subovici Signed and sealed this 17th day of March1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

